libao is a cross-platform audio library that allows programs to
output audio using a simple API on a wide variety of platforms.
On FreeBSD, it currently supports:
   * null output
   * raw output
   * AU files
   * WAV files
   * OSS (Open Sound System)
   * ESD (ESounD or Enlightened Sound Daemon)
   * aRts (KDE sound server)

WWW: http://www.xiph.org/ao/